nLab: Ordinal
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Comprehensive reference on ordinals in category-theoretic context
More resources on Ordinals
Cantor's Paradise: Ordinal Numbers Explained
Accessible article on ordinals from beginner to advanced
Stanford Encyclopedia of Philosophy: Set Theory
Section on ordinals and transfinite recursion
Set Theory
Learn ordinal numbers with William Hamilton's Set Theory course! Explore fundamental concepts and deepen your understanding.
mathworld.wolfram.com
MathWorld is Wolfram’s comprehensive online mathematics encyclopedia offering concise, authoritative articles that define and explain mathematical concepts, theorems, and formulas. It covers topics across math, including set theory and ordinal numbers, with explanations, examples, and references.
ocw.mit.edu
MIT OpenCourseWare (OCW) is a free, openly accessible repository of MIT course materials—lecture notes, assignments, exams, and sometimes video lectures—spanning a wide range of subjects. It enables self-paced study and exploration of topics such as mathematics that may cover ordinal concepts.
Introduction to Mathematical Thinking
Learn how to think the way mathematicians do – a powerful cognitive process developed over thousands of years. Mathematical thinking is not the same as doing mathematics – at least not as mathematics is typically presented in our school system. School math typically focuses on learning procedures to solve highly stereotyped problems. Professional mathematicians think a certain way to solve real problems, problems that can arise from the everyday world, or from science, or from within mathematics itself. The key to success in school math is to learn to think inside-the-box. In contrast, a key feature of mathematical thinking is thinking outside-the-box – a valuable ability in today’s world. This course helps to develop that crucial way of thinking.